This invention relates to a throttle valve position detecting apparatus for use with an internal combustion engine having two throttle valves located in series within an engine induction passage and, more particularly, to a throttle valve position detecting apparatus for correcting a deviation of two sensor signals for the same throttle valve positions.
For example, Japanese Patent Kokai No. 62-192824 discloses a traction control apparatus for use with an internal combustion engine having first and second throttle valves located in series within an engine induction passage. The first throttle valve is associated through a mechanical linkage with an accelerator pedal. The second throttle valve is associated with a throttle valve actuator controlled by an electric control unit. The control unit controls the second throttle valve to reduce an engine output so as to hold a slip factor within a predetermined range when slip occurs for the vehicle drive wheels. For this purpose, the traction control apparatus produces a target value for the second throttle valve position. A first throttle sensor is provided for deriving a first sensor signal indicative of a first throttle valve position and a second throttle sensor is provided for deriving a second sensor signal indicative of a second throttle valve position. The first sensor signal is used to determine the amount of fuel delivered to the engine. Normally, the greater the first throttle valve position, the greater the amount of fuel delivered to the engine. The second sensor signal is compared with the calculated target value for the second throttle valve position to provide a closed loop control signal in response to a sensed deviation of the detected throttle valve position from the target throttle valve position. The closed loop control signal is used to drive the throttle valve actuator so as to move the second throttle valve in a direction zeroing the sensed deviation.
If the first throttle valve opens for engine acceleration with the second throttle valve being closed to provide a traction control, the amount of fuel metered to the engine will increases in spite of the fact that the amount of air to the engine is limited by the second throttle valve. As a result, an overrich air/fuel mixture enters the engine, causing degraded fuel economy and degraded engine operating performance. In order to avoid the problem, it may be considered to make the fuel delivery control based upon a smaller one of the first and second sensor signals. However, another problem arises when there is a deviation between the first and second sensor signals for the same throttle positions.
Referring to FIG. 1A, there is shown a first case where the first and second throttle valves occupy the same minimum position .theta.1 when they are fully closed, but the second sensor signal V2 has a value V20 when the second throttle valve is at the minimum position .theta.1, the value V20 being greater than the value V10 of the first sensor signal V1 produced when the first throttle valve is at the minimum position .theta.1. As can be seen from FIG. 1A, the value V21 of the second sensor signal V2 is greater than the value V11 of the first sensor signal V1 in spite of the fact that the second throttle valve position at which the second sensor signal V2 has the value V21 is less than the first throttle valve position at which the first sensor signal V1 has the value V11. If the fuel delivery control is based upon the smaller one of the first and second sensor signals during a traction control, an overrich air/fuel mixture will enter the engine, causing engine stall.
Referring to FIG. 1B, there is shown a second case where the first and second throttle valves occupy different minimum positions .theta.10 and .theta.20, respectively, when they are closed fully, the minimum position .theta.10 of the first throttle valve being less than the minimum position .theta.20 of the second throttle valve. As can be seen from FIG. 1B, the second sensor signal V2 has a value V22 less than the value V12 of the first sensor signal V1 in spite of the fact that the the position at which the second sensor signal V2 has the value V22 is greater than the position at which the first sensor signal V1 has the value V12. If the fuel delivery control is made based upon the smaller one of the first and second sensor signals when the accelerator pedal is released to close the first throttle valve, an overrich air/fuel mixture will enter the engine, causing engine stall.